This invention relates to a method of improving the fabrication of etched semiconductor devices by using a patterned adhesion promoter layer over a hydrocarbon planarization material. More specifically, the present invention improves the bonding of a metal interconnect layer to a hydrocarbon planarization material, such as polyimide, by inserting an adhesion promotion layer, such as silicon nitride, between the hydrocarbon planarization material and the metal interconnect layer.
During the fabrication of integrated circuit chips, various layers, such as insulating, metallizing and passivating layers, are deposited on the surface of a semiconductor substrate. These various layers should exhibit some degree of adhesion to one another. Poor adhesion between the layers may allow moisture or other impurities to penetrate the seams between the layers, causing corrosion or other impurity-induced phenomena that adversely impacts the performance of the integrated circuit. Similarly, poor adhesion between a metallizing layer and the underlying layer also may result in poor wire bonding because the deposited metal layer is not sufficiently bonded to the underlying layer. Accordingly, it is important that the bond between the deposited layer and the underlying layer be sufficiently strong so that the deposited layer does not separate from or flake off of the underlying layer.
During the fabrication of integrated circuit chips and oxide vertical cavity surface emitting lasers, various stages of dry or wet etching are performed to pattern and remove portions of the thin films that are deposited on the semiconductor substrate. During this process, a thin film is usually deposited over an etched surface to protect it. Typically, a hydrocarbon planarization material such as polyimide is used in this process. Polyimide is a well-known insulating material, and it is widely used as a passivation film or an inter-level insulating film between upper and lower wiring layers. A polyimide film can be formed on a semiconductor substrate through a spin-coating method and subsequently cured or hardened in a high temperature heat-treatment process. After the polyimide film is cured, a metal interconnect layer is often deposited and patterned on the surface of the polyimide film. A wire bond may be attached to the surface of the metal interconnect layer, and the wire bond functions to electrically connect the semiconductor device to the external environment. However, poor bonding often results between the metal interconnect layer and the polyimide layer because the polyimide layer does not provide a robust bonding surface for the metal interconnect layer. Poor adhesion of the interconnect metal to the polyimide layer typically creates a wire bonding problem, which is the inability to reliably and robustly connect a wire bond to the thin metal interconnect layer. A high failure rate of wire bonds can adversely effect the performance of the semiconductor device.
Various techniques have been attempted in an effort to improve the bonding between the metal interconnect layer and a hydrocarbon planarization material such as polyimide. These techniques include: (1) roughening the surface of the hydrocarbon planarization material to provide a better adhesion surface; (2) de-scumming the surface of the hydrocarbon planarization material in an effort to improve adhesion; and (3) varying the curing time and temperature bake of the hydrocarbon planarization material. However, none of these methods have produced a reliable means to improve the adhesion between the metal interconnect layer and the hydrocarbon planarization layer.
Accordingly, there exists a need in the art of semiconductor fabrication to provide a method to improve the adhesion between a metal interconnect layer and a hydrocarbon planarization material such as polyimide.
In view of the above-stated disadvantages of the prior art, it is an object of the present invention to provide a method for improving the adhesion of a metal interconnect layer to a hydrocarbon planarization material such as polyimide.
It is another object of the present invention to provide a fabrication process that is compatible with the planarization process that is used in a typical semiconductor manufacturing process.
It is another object of the present invention to improve the wire bonding strength of a metal interconnect layer.
It is another object of the present invention to improve the reliability and robustness of a semiconductor device by improving the bonding between a metal interconnect layer and a polyimide layer.
These and other objects are achieved by the present invention which is a method for improving the fabrication of etched semiconductor devices. The method includes the steps of depositing a hydrocarbon planarization material over a substrate; depositing an adhesion promoter over the hydrocarbon planarization material; patterning the adhesion promoter so as to form an adhesion promoter pad over a portion of the hydrocarbon planarization material; and deposition a first metal over the adhesion promoter pad.
These steps describe a process, according to an embodiment of the invention, for improving the adhesion of a metal interconnect layer to a hydrocarbon planarization material such as polyimide is described below. This process may be suitable in the fabrication of various semiconductor devices, including vertical cavity surface emitting lasers.
Moreover, although an embodiment of the invention utilizes silicon nitride as an adhesion promotion layer between the metal interconnect layer and polyimide layer, other substances also may be used in place of silicon nitride. For example, silicon oxide may be used in place of silicon nitride throughout the entire process steps. Silicon oxide has similar characteristics as silicon nitride and functions as a robust adhesion promotion layer between the metal interconnect layer and the polyimide layer. Furthermore, although an embodiment of the invention utilizes polyimide as the hydrocarbon planarization material, other hydrocarbon planarization material that have similar characteristics may be used.